Bearing apparatus and producing method thereof

ABSTRACT

A bearing apparatus includes a hollow shaft provided around an outer peripheral surface with a bearing fitting region, and a rolling bearing having an inner ring fitted around the bearing fitting region of the hollow shaft. A shaft end of the hollow shaft is bent outwardly in a diametrical direction, thereby being caulked on an outer end surface of the inner ring. The bearing fitting region has a hardened layer in a region from a first position corresponding to an inner end surface of the inner ring of the rolling bearing to a second position before a position corresponding to an outer end surface of the inner ring, and has a non-hardened layer in another region from the outer end surface corresponding position of the inner ring to the shaft end. The second position representative of a caulked side end portion of the hardened layer is defined based on a predetermined relational expression.

REFERENCE TO RELATED APPLICATION

This is a divisional application and hereby incorporates by referencethe entire disclosure of application Ser. No. 09/902,245 now U.S. Pat.No. 6,672,769, filed Jul. 10, 2001.

BACKGROUND OF THE INVENTION

The present invention relates to a bearing apparatus and a producingmethod thereof, and more particularly, to a bearing apparatus and aproducing method thereof which are preferably used for a hub unit for avehicle such as an automobile.

A hub unit for a vehicle will be explained. The hub wheel has a hollowshaft. An inner ring of a rolling bearing is mounted to an outerperiphery of the hollow shaft by press-fit. A shaft end of the hollowshaft is caulked on the outer end surface of the inner ring by bendingthe shaft end outwardly in a diametrical direction. The bearing isprevented from slipping off from the hollow shaft by this caulkedportion. A pre-load is applied to the inner ring of the bearing by thiscaulking.

A load is applied to the hollow shaft by the pressure-fit of the innerring of the bearing. The hollow shaft is formed around its outerperiphery with a hardened layer due to heat by quenching or the like inorder that the hollow shaft has the structure that can bear the load. Onthe other hand, the shaft end of the hollow shaft remains in a stage ofbeing caulked on the outer end surface of the inner ring, i.e., theshaft end is not hardened.

A range of the hardened layer formed on the outer periphery of thehollow shaft is limited to a certain degree.

However, in the range where the hardened layer is formed, a position ofthe caulked side end portion in the axial direction is not clearlydefined. Thus, when it is processed to be hardened, the position of thecaulked side end portion of the hardened layer in its add is prone to bean incorrect position closer to an outer end or to inner end in theaxial direction from the limited range.

If the position of the end portion in the axial direction of thehardened layer is positioned incorrectly with respect to the hollowshaft, a gap may be generated between an inner peripheral surface of theinner ring and an outer peripheral surface of the hollow shaft caulkedon the outer end surface thereof in some cases. This gap deterioratescreep resistance.

Therefore, a caulking auxiliary jig is previously inserted on the sideof the inner periphery of the hollow shaft before caulking, therebypreventing the gap from being generated. Further, after the caulking,the inner periphery of the hollow shaft is again worked. Such agap-preventing operation of the hollow shaft increases the number ofproducing steps and cost of the hub unit.

SUMMARY OF THE INVENTION

Thus, it is a main object of the present invention to provide a bearingapparatus of a hub unit, and the like, for a vehicle, capable ofappropriately managing a position of an end portion, in the axialdirection, of a hardened layer formed on an outer periphery of a hollowshaft.

Other objects, features and merits of the present invention will beapparent from the following description.

The present invention is, in sum, described as follows. A bearingapparatus of the present invention includes a hollow shaft providedaround its outer peripheral surface with a bearing fitting region, and arolling bearing having an inner ring fitted around the bearing fittingregion of the hollow shaft. A shaft end of the hollow shaft is bentoutwardly in a diametrical direction, thereby being caulked on an outerend surface of the inner ring of the rolling bearing.

The bearing fitting region has a hardened layer in its region from aninner end surface corresponding position of the inner ring of therolling bearing to a portion before an outer end surface correspondingposition. The bearing fitting region further has a non-hardened layer inits region from the portion before the outer end surface correspondingposition of the inner ring to the shaft end of the hollow shaft.

A position of a caulked side end portion of the hardened layer isdefined based on the following relational expression (1):((A−C−D)Y/E)≦X<(A−C)  (1)wherein A represents a width in the axial direction of the inner ring, Crepresents a chamfering length in the axial direction in the outer endsurface of the caulked side of the inner ring, D represents a chamferinglength in the axial direction in an outer end surface of the inner ring,E represents a thickness of the hollow shaft, X represents a distancefrom a position of the chamfering length D to the caulked side endportion of the hardened layer, and Y (<E) represents a hardeningtreatment depth.

With this defining expression, appropriate hardening treatment can becarried out by applying concrete numerical values to the respectivelength in the axial direction of the inner ring and the thickness of thehollow shaft. Further, it is possible to reduce the number of steps andtime of the producing operation of the bearing apparatus, such as a hubunit, and to enhance the productivity.

In the present invention, preferably, the hollow shaft is a hub wheel,the rolling bearing is a double row angular contact ball bearing withvertex of contact angles outside of bearing or a double row taperedroller bearing with vertex of contact angles outside of bearing.

These and other objects, as well as advantages, of the invention willbecome clear by the following description of preferred embodiments ofthe invention with reference to the accompanying drawings, wherein likecomponents are indicated by the same numerals.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a vertical sectional view of a hub unit before caulkingaccording to a preferred embodiment of the present invention;

FIG. 2 corresponds to FIG. 1 and is a vertical sectional view aftercaulking;

FIG. 3 is an enlarged sectional view of an essential portion in FIG. 1;

FIG. 4 is an enlarged sectional view of an essential portion accordingto another preferred embodiment of the invention; and

FIG. 5 is an enlarged sectional view of an essential portion accordingto another preferred embodiment of the invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

A hub unit for a driving wheel of a vehicle as a bearing apparatusaccording to a preferred embodiment of the present invention will beexplained with reference to FIGS. 1 to 3.

A hub unit 10 includes a hub wheel 11 and a bearing 12.

The hub wheel 11 includes a flange 13 and a hollow shaft 14. A wheel(not shown) is mounted to the flange 13. The hollow shaft 14 has abearing fitting region comprising a large-diameter outer peripheralsurface and a small-diameter outer peripheral surface. The bearing 12 isfixed to the bearing fitting region.

A shaft end 14 a of the hollow shaft 14 is bent outwardly in adiametrical direction from a state shown in FIG. 1 by rolling caulkingand is plastically deformed. With this operation, the shaft end 14 a iscaulked on an outer end surface of an inner ring 15 of an angularcontact ball bearing 12 as shown in FIG. 2.

The bearing 12 is a double row angular contact ball bearing with vertexof contact angles outside of bearing as one example of an inclinedrolling bearing. The bearing 12 includes an inner ring (first innerring) 15 having a single orbit which is fitted around the small-diameterouter peripheral surface of the bearing fitting region of the hollowshaft 14, a single outer ring 16 having two rows of orbit grooves, aplurality of balls 17 arranged in two rows, and two cages 18.

The large-diameter outer peripheral surface of the bearing fittingregion of the hollow shaft 14 of the hub wheel 11 is one inner ring(second inner ring) of the bearing 12. An inner ring of a common singleraw angular contact ball bearing is used as the inner ring 15 as it is.

The outer ring 16 is provided around its outer periphery with a flange19.

The caulking operation of the hub unit 10 will be explained.

The shaft end 14 a of the hollow shaft 14 is caulked on the outer endsurface of the inner ring 15 from a state shown in FIG. 1 to a stateshown in FIG. 2. Thereafter, the hub unit 10 is mounted between a driveshaft 20 and a knuckle (or carrier) 21 of the vehicle. That is, thehollow shaft 14 of the hub wheel 11 is spline-fitted into the driveshaft 20 and coupled by a nut 22. The flange 19 of the outer ring 16 ofthe bearing 12 is non-rotatably coupled to the knuckle (or carrier) 21by means of a bolt 23.

Features of the present embodiment will be explained with reference toFIG. 3.

The outer end surface of the inner ring 15 of the bearing 12 has aninner peripheral angle portion 15 a. The inner peripheral angle portion15 a is roundly chamfered, e.g., from a center O through ¼ circumferenceof radius of curvature C. An inner end surface in the inner ring 15 ofthe bearing 12 has an inner peripheral angle portion 15 b. The innerperipheral angle portion 15 b is roundly chamfered, e.g., from thecenter O through ¼ circumference of radius of curvature C.

The inner peripheral angle portion 15 a has a chamfering-start point 15c. The chamfering-start point 15 c is a bending-start point when theshaft end 14 a of the hollow shaft 14 is bent outwardly in a diametricaldirection around the outer end surface of the inner ring 15. The innerperipheral angle portion 15 b of the inner ring 15 has achamfering-start point 15 d.

In the bearing fitting region of the hollow shaft 14, hardened layers 24a and 24 b are formed from the large-diameter outer peripheral surfaceto the small-diameter outer peripheral surface thereof as shown withcross hatchings in the drawings.

The hardened layer 24 b formed on the small-diameter outer peripheralsurface into which the inner ring 15 of the bearing 12 is fitted ishardened through a required depth from its surface by thermal treatmentsuch as quenching in a region from a position (first correspondingposition) corresponding to an inner end surface of the inner ring 15 toa portion before a position (second corresponding position)corresponding to an outer end surface.

A range of the hollow shaft 14 from its portion before the secondcorresponding position to the shaft end 14 a of the hollow shaft 14 isnon-hardened layer. With this layer, it is possible to caulk the shaftend 14 a with respect to the outer end surface of the inner ring 15outwardly in a diametrical direction.

Here, the portion before the second corresponding position is defined asa position (X) of the caulked side end portion of a hardened layer 24.

The position (X) of the caulked portion is defined between thebending-start point 15 c and a position which is determined by athickness (E) of the hollow shaft 14 and a fitting region length (A−C−D)of the hollow shaft 14 into the inner ring 15 in the small-diameterouter peripheral surface with respect to at least predeterminedhardening treatment depth (Y).

The definition of the position (X) of the caulked side end portion of ahardened layer 24 b will be explained in detail.

A length in the axial direction of the inner ring 15 of the angularcontact ball bearing 12 is defined as (A), a chamfering length in theaxial direction of the outer end surface of the inner ring 15 is definedas (C), a chamfering length in the axial direction of the inner endsurface of the inner ring 15 is defined as (D), an axial thickness ofthe hollow shaft 14 is defined as (E), a distance from the position ofthe chamfering length (D) in the inner ring 15 to the caulked side endportion of the hardened layer 24 b is defined as (X), and a hardeningtreating depth is defined as (Y). However, when the inner peripheralsurface of the hollow shaft 14 is formed with female spline as in thisembodiment, the axial thickness (E) is a thickness from the outerperiphery of the hollow shaft 14 to the bottom of the tooth of thefemale spline.

The position (X) of the caulked side end portion of the hardened layer24 b is defined in a range shown with the following expression (1).((A−C−D)Y/E)≦X<(A−C)  (1)

In the expression (1), the left side term (A−C−D) Y/E is based on acondition that the fitting region length between the hollow shaft 14 andthe inner ring 15 when the hollow shaft 14 is caulked and deformed isdefined as (A−C−D), the axial thickness of the hollow shaft 14 isdefined as (E)mm, the position of the caulked terminal end of thehardened layer 24 b is defined as (X) mm, and the hardening treatmentdepth of the hardened layer 24 b is defined as (Y) mm. In this case,according to experiments and calculations by the present inventors, anexpression (A−C−D):E=X:Y is established. From this expression, therelation (A−C−D) Y/E is established.

TABLE 1 Bearing Bearing (1) (2) Desk checking Size A 18 22 mm C 4.5 4.5D 2.5 2.5 E 5 3.5 Y 2.5 2.5 X (min.) (A − C − 5.5 10.7 D)*Y/E X (max.) A− C 13.5 17.5 X (min.) + D 8.0 13.2 X (max.) + D 16.0 20.0 Result oftest X + D 0 x x On interface mm 2 x x between inner 3 x x ring andshaft 5 x x O: no clearance 8 O x exists 10 O x x: clearance 13 O Oexists 15 O O 17 x O 20 — O 22 — x

In Table 1, “Result of test” shows the result after changing the valueof X by each size (A, C, D, E, and Y) of the bearing shown in “Deskchecking.” X(min) represents the minimum value of X, and X(max)represents the maximum value of X. The bearings (1) and (2) are onlydifferent in size, and they are employed in the test in order to obtainthe relational expression (1) that satisfies in the cases of bearingswith different sizes.

That is, when the hardened layer 24 b is formed on the hollow shaft 14,if the length in the axial direction of the hollow shaft 14 is long, thetreatment width of the hardened layer 24 b in the axial directionbecomes long correspondingly. If the shaft thickness (E) of the hollowshaft 14 is increased, the load bearing capacity from the inner ring 15is increased and thus, the thickness (Y) of the hardened layer 24 b maybe shallow correspondingly.

Therefore, from the left side term (A−C−D) Y/E of the above expression(1), the position (X) of the caulked side end portion of the hardenedlayer 24 b is proportional to the hardening treatment depth (Y) and thefitting region length (A−C−D) between the hollow shaft 14 and the innerring 15, and is inversely proportional to the shaft thickness (E) of thehollow shaft 14.

From the above reasons, it is possible to harden the hollow shaft 14 bydefining the position (X) of the caulked side end portion of thehardened layer 24 b in the region of the expression (1).

The hollow shaft 14 of the hub wheel 11 has low load bearing capacity ofthe inner ring 15. Therefore, the position (X) of the caulked side endportion of the hardened layer 24 b is important. Thus, the hollow shaft14 by defining the position (X) of the caulked side end portion of thehardened layer 24 b is defined as a position defined based on the lengthin the axial direction and axial thickness of the hollow shaft 14 whichis caulked and deformed in shortest. With this design, it is possible tooptimize the caulking load of the shaft end of the hollow shaft 14 withrespect to the outer end surface of the inner ring 15, and to optimizethe load bearing capacity of the inner ring 15.

From the above reasons, in the small-diameter outer peripheral surfaceof the hollow shaft 14, the range from the position (X) to the shaft endis non-hardened layer. Therefore, at the time of caulking, no gap isgenerated between the small-diameter outer peripheral surface and theinner peripheral surface of the inner ring 15 in that range, and thehollow shaft 14 is caulked with respect to the outer peripheral surfaceof the inner ring 15. The range from the first corresponding position tothe position (X) is formed as the hardened layer 24. Therefore, no gapis generated between the small-diameter outer peripheral surface and theinner peripheral surface of the inner ring 15 in that range, and thehollow shaft 14 is caulked with respect to the outer peripheral surfaceof the inner ring 15. As a result, the hub unit 10 has excellent creepresistance.

When the hub unit 10 is produced, it is unnecessary to previously insertthe caulking auxiliary jig into the inner diameter side of the hollowshaft 14 to prevent a gap from being generated, and to work the innerdiameter of the hollow shaft 14.

For these reasons also, the structure of the hub unit 10 is suitable formass production in which the number of steps and time of the productioncan be reduced.

In the above case, if the axial chamfering length of the innerperipheral angle portion of the outer end surface of the inner ring 15is added to the correlation in the definition of the shortest positionof the caulked side end portion of the hardened layer 24 b, it ispossible to manage the position of the caulked side end portion of thehardened layer 24 b more appropriately.

The present invention is not limited to the above embodiment, andvarious applications of modifications are possible.

(1) According to the present invention, as shown in FIG. 4, the abovehardened layer 24 b can also be applied to a hub unit in which the firstinner ring 15 and the second inner ring 15 e have a bearing 12 disposedadjacent thereto in its axial direction. In this case, both the firstinner ring 15 and the second inner ring 15 e are fitted around thesmall-diameter outer peripheral surface of the hollow shaft 14. Theshaft end of the hollow shaft 14 is caulked on the outer end surface ofthe first inner ring 15.

(2) In the invention, a double row tapered roller bearing with vertex ofcontact angles outside of bearing may be used. An inner ring in thatcase may comprise one inner ring and an inner ring and another innerring which is integrally formed on an outer peripheral surface of thehollow shaft, or may comprise two inner rings adjacently disposed in theaxial direction, like the double row angular contact ball bearing withvertex of contact angles outside of bearing. The above hardened layer 24can also be applied to a hub unit having the tapered roller bearing withvertex of contact angles outside of bearing.

(3) The present invention is not limited to the hollow shaft 14 which ishollow in the axial direction, and as shown in FIG. 5, the hardenedlayer 24 b can also be applied to a hub unit having a bottomed shaft 14a.

(4) The present invention is not limited to the driving wheel of avehicle, and the hardened layer 24 b can also be applied to a hub unitfor a follower wheel of the vehicle.

(5) An inner periphery of the hollow shaft 14 of the hub wheel 11 isformed with the female spline 14 b meshing with male spline formed on anouter periphery of the drive shaft 20 for fitting the drive shaft 20into the hollow shaft 14.

In order to couple the hollow shaft 14 and the drive shaft 20 to eachother with mechanically necessary strength, it is preferable that thespline 14 b is formed in the axial direction on the inner periphery ofthe hollow shaft 14. With this design, an end of the spline 14 b isclose to the caulked portion. According to this design, in a regionclose to the caulked portion, the male spline of the drive shaft 20 isprone to be deformed such as to be shrunk in the diametrical directionin such a degree that the male spline of the drive shaft 20 can not befitted into the female spline easily when the caulked portion iscaulked. This deformation could reach 50 mm in the diametrical directionin some cases. To avoid this deformation, the following first and secondproducing methods are proposed.

In the first producing method, the spline 14 b is subjected to a primaryworking such as spline broach with respect to the inner periphery of thehollow shaft 14 before caulking, and the spline 14 b on the innerperiphery of the hollow shaft 14 after caulking is subjected to asecondary working such as the spline broach. In the case of thesecondary working, a deformed portion of the spline 14 b formed by theprimary working generated during the caulking working is subjected tocorrecting working such as plastically deformation so that the spline ofthe drive shaft 20 can be fitted.

In the second producing method, the inner periphery of the hollow shaft14 is not formed with the spline 14 b before caulking, and the innerperiphery of the hollow shaft 14 is formed with the spline 14 b bymechanical working such as spline broach after caulking.

With any of the methods, it is possible to enhance the shape precisionof the spline 14 b formed on the inner periphery of the hollow shaft 14after caulking. Therefore, it is possible to easily fit the splineformed on the outer periphery of the drive shaft 20 to the spline 14 b.

(6) In the present invention, a structure in which the first inner ring15 and the second inner ring 15 e of the common single row angularcontact ball bearing may be subjected to the spline broach as in thesame manner as that of above (5) with respect to the spline 14 b to theinner periphery of the hollow shaft 14 as partially shown in FIG. 4.

While there has been described what is at present considered to bepreferred embodiments of this invention, it will be understood thatvarious modifications may be made therein, and it is intended to coverin the appended claims all such modifications as fall within the truespirit and scope of this invention.

1. A producing method of a bearing apparatus, said bearing apparatuscomprising a hollow shaft provided around its outer peripheral surfacewith a bearing fitting region, and a rolling bearing having an innerring fitted around said bearing fitting region of said hollow shaft,said hollow shaft has a female spline which is fitted to a male splineformed on an outer peripheral surface of a drive shaft, a shaft end ofsaid hollow shaft being bent outwardly in a diametrical direction,thereby being caulked on an outer end surface of said inner ring of saidrolling bearing, wherein said method comprising the steps of: subjectingan inner peripheral surface of said hollow shaft to a primary workingfor forming said female spline; caulking the shaft end of said hollowshaft on the outer end surface of said inner ring of said rollingbearing after said female spline is formed; and subjecting said femalespline of said hollow shaft to a secondary working after caulking, andwherein said secondary working is a correcting working for correcting adeformed portion generated by said caulking so that said female splineformed by said primary working can be fitted to the male spline of saiddrive shaft.
 2. A producing method of a bearing apparatus, said bearingapparatus comprising a hollow shaft provided around its outer peripheralsurface with a bearing fitting region, and a rolling bearing having aninner ring fitted around said bearing fitting region of said hollowshaft, said hollow shaft has a female spline which is fitted to a malespline formed on an outer peripheral surface of a drive shaft, a shaftend of said hollow shaft being bent outwardly in a diametricaldirection, thereby being caulked on an outer end surface of said innerring of said rolling bearing, wherein said method comprising the stepsof: caulking the shaft end of said hollow shaft on an outer end surfaceof said inner ring; and forming a female spline on an inner peripheralsurface of said hollow shaft after caulking.